Microwave amplifier of the magnetron type



June 2, 1953 J. B. H. KUPER 2,640,951

MICROWAVE AMPLIFIER 0F THEMAGNETRON TYPE Filed June 25 1949 INVENTOR JAMES B K UPE E ATTORNEY Patented June 2, 1 953 MIUEQWHYEAMPLIEIERI OETHE MAGNETRONQ James"Bmwn Horne Kuper: Ba'ynortg N YL, va signorto fiiternational Stamlartl' Electi-icElias;-

Thismventionlrelates to eletrondis'charge-de vices and is particularly directd'ioy devices of the magnetron: type: More'rspecifioally this in:-

mention is directed'to devices which have somemof segment i type arezremarkahlit' fiieient"generators to: 3" centimeter bandit Eart'i of such; high efiiiciencies 7' must? be? ascribed? to then fact that any one electron or:group-voffeleetrons interact with theielctromagnetic'iiem,fonaz'comnaratively long? time; severalffradio; frequencwcyelesr being usual? to: be; contrasted? with" the"; klystron' type generator where the interaction time? between ttie'electrons'rofla beam andithe radiozfrequency field is. of the*ordernf orre halfipcyclefori'lessr' The object?ofthis inventiorr-istan.amplifienin whielrthe high eie'ctronicteflicincymf. tliamage netron'generator' istutllized f A: more rgeneral object of thisirinvention isz-an amplifier of" high efllieney the mierowave range:

'lfli' 'amplifierFaeeordirig toftl'iis:inventiorrcom prises ianfelongated tuliularicatliode coaxial witir a'itt'ib'ular anod'e: structure off'equal length." fir addition .totlie radia-lEelctritandaxizl magnetic between a tubular cathode and anode-with: a.

numberot' eavityresonators*opennig omthe spaee,

and electricand magnetieifields io'f-= the: properv magnituds' and-idirections to i' roduee; according-i to one conception,- traveling space charges or? electrombunches whioh't travel through the -;e1e'- trio radiofrequencwfieids attheicavity" openings?- Fortunately. the mean" electrons L entrain" in: the proper phase relations with tn adiovirequen'cy fieldto yield as much as '50 to percent of tli'e kinetic energy, derived from" the" clir'ect current field, to: the" radio. ffequen'eyj 'fieldt Allv of this radio frequency energyyiminus" the eisiei gat losses ofthe system; may 'b'er'em'ovedand utilized? As in all generators, self-sustained oscillatknrs require sufficient: radio frequency energy to" be feduback'fromione pointiinithe system to. another;

for a given" transcomluctance," to OVEICOTYlG the system losses between thepoints. ventionalmagnetronwitltai cl'osedf circie ofcavity resonators; ea'ch cavity? resonator: is? equally coupled to" the. adjacent resonators" on either side-and 'therauio'tfrequencszoutputmay beetafien" from any; one off the":identical resonatorsiby arr antenna-1160p or probe? Efi'ergyfflowsrtowarn' the output 'resonatorfrom.aroimc1the.circle or 'reso nators; the first fintthe series for -resonatorsbeing conveniently adjacent the." output' resonator" so that'th'e imen-tioned'feedFbaclenergyi easily, moves directly; from"the=butput""toitiie input ofth e series ofiesonatorsand oscillationsfa-resustained-I Now, aocordingptofanimportant feature ofttiis inventiongth'efeedback" energyj-fronrltiie' output resonator: is; reduced. and; controlled? or elimia nated,-and..1energy, from; an? outside sourceft'o be amplified, is. fedT-into; the "mnutiresonator'; The efficiencies: of;- the .magnetronmscilhtbr ;may; now. bezrealized in an amplifier;

The :particular: embodimentoof this; invention shown inlthew drawinggoomprises alspirai arrangea ment. of cavity-resonatorsgaboutzvtliestubularicatha ode? I and. the: intervening; coaxial. interaction spate 2a The? anode. structure-.- may; comprise; a cylindrical zblOGkL- 3 tot such metal ias: copper; with a serieszvot holes 4-; drilled. lengthwise .of ithehloclt. Radial .'.slots',-. 5; also.- extending lengthwise of the block, ,are:mi-lledato 'communioatemwith.eaehlhol and. lthei center hore? on interactiomspace; .of. the block. Fulani/, a l rectangular; helical 'cutt 6.1 is. made in: th-eawall of the center: bore the depth of;- thetcutgmeasured in a: radial rlireetio'n, being2 sufficient to reachtto or :b'eyondlthe@outeriextremie ties of the holes 4. It now appears that theianode structurecontains .ae series-rot, cavity! res enators with slots 511811051132- disposedzabout atliecenteribora and: that *the a. number: oft. resonatorsse mayo be creased tosariy1desireddnumbemmereiyi-bminereast ing the number of helical convolutions about the center bore. To prevent field interactions between adjacent ends of the end-to-end resonators, an edge-wound metal strip 1 is formed and threaded into the helical cut. The inside diameter of the wound strip should substantially coincide with the bore diameter, and the outer edge of the strip should make at least radio frequency contact with the wall of the block.

The cathode l is an indirectly heated sleeve supported at opposite ends on lead-in conductors 8 and 9, and is exteriorly coated with electron emissive material. To confine emission to the spaces opposite the cavity slots, the coated material may be applied barber-pole fashion to the sleeve. Insulated end plates and II are provided for establishing an electric field parallel to the magnetic field and axially to the cathode.

The lead-in conductors l2 and [3 support the plates.

A second edgewound strip [4 is preferably inserted alongside the shield strip and is sufficientl-y rigid to be slidable as a unit lengthwise of the anode structure so that the spaces at the ends of the cavities may be adjusted. A dielectric rod I5 is connected to strip-H and mounted on bellows through the envelope of the tube to effect sliding of the strip. A limited range of tuning may thus be effected.

The loops I6 and Hare mounted, respectively, in the two end resonators and are coupled through coaxial lines 18 and [9 to input and output circuits.

Magnetic pole pieces 20 and 2! are arranged at the ends of the cathode to provide an axial magnetic field for causing the electrons to follow spiral paths.

, To operate, a direct current voltage is applied between the cathode and anode and a direct current magnetic field is applied with poles at the ends of the cathode. The magnitudes of the electric and magnetic field are comparable to the fields that would be applied to a magnetron of corresponding radial dimensions to produce circult electron trajectories in the anode-cathode space. Now, a potential gradient between end plate [0 and I I will give axial velocity to the electrons and the value thereof may be adjusted so that the pitch of .the spiral path will equal the mean pitch of the cavity resonator slots.

' In operation, signals within the tunable range of the cavity resonators are applied to loop [6 in the lower end resonator. Bunching of the electrons in the electric ,and magnetic fields in the anode-cathode space immediately commences under the influence of the signal voltage. The resulting electron bunches and electromagnetic waves of signal frequency travel in helical paths past and through the successive cavity resonators toward the output resonator. The strength of the axial electric field between plates I0 and H must be adjusted with respect to that of the radial electric and magnetic fields so that the rotating space charge will take a helical turn with a velocity close to that of the travelling wave, and the direct-current to alternating-current transfer of energy continues until at the output cavity the travelling electromagnetic waves have attained the maximum values permissible within the structural and electrical parameters of the amplifier. High level radio frequency energy is removed by loop H.

To prevent reflections from the output or end cavity resonator toward the input end and to minimize standing waves and the danger of radio frequency voltage breakdown, it is important that 4 the load be properly matched, as to impedance and Q, to the output cavity resonator. Local feedback between resonators must also be prevented, and when necessary, resistive losses may be introduced as by roughening or otherwise treating the surfaces of the resonators or by the selection ofanode material having a somewhat lower specific conductance. With feedback kept below the level necessary for self support oscillations, the amplitude of the output voltage will faithfully follow the signals applied to the input resonator, and the over-all voltage gain may be limited only by the radio frequency insulation at and around the output resonator.

Positive regeneration may of course be employed to increase gain when desired. Feedback could be through any of the known transmission lines which could be adjusted for regulating amplitude and phase of the feedback energy.

While there has been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

Q What I claim is.

1. An electron discharge device for amplification of high frequency energy comprising an elongated electron emitting cathode, an anode including a plurality of cavity resonators located in helical formation about said cathode, said resonators being coupled together in series along said helical formation, means adjacent said cathode to produce a magnetic field axially of said source, platesinsulated from said cathode and anode, positioned at the ends of said cathode to produce an electric field axially of said source whereby said electrons will follow helical paths about said source, and output coupling means for the resonator at one end of said helix.

2. An electron discharge device comprising an elongated electron emitting cathode electrode. an anode including a plurality of high frequency resonators located in a helicalformation about said cathode electrode, said resonators being coupled together in series along said helical formation, meansfor producing a, magnetic field through said device parallel to said cathode electrode, means for producing an electric potential field parallel to said cathode electrode whereby electrons from said cathode electrode traverse a spiral path parallel to said cathode electrode, and an output terminal coupled with one of said resonators. i

3. An electron discharge device according to claim 2, wherein said means for-producing-anelectric field comprise electrodes spaced from said anode at opposite ends thereof and coaxial with said cathode electrode.

4. An electron discharge device comprising an elongated electron emitting cathode, an anode including a plurality of high frequency resona-' tors located in a helical formation about said cathode, longitudinal electric and magnetic fields producing means located adjacent said cathode to cause said electrons to follow helical paths thereabout, shielding means located between the turns of said helical formation of resonators for isolating high frequency fields in said resonators that are adjacent one another in separate turns of said helical formation of said resonators, and output coupling means .coupled to one of said resonators.

5. An electron discharge device comprising an References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Potter July 5, 1938 Thompson Aug. 26, 1941 Smith Apr. 13, 1948 Garner July 26, 1949 

